1. Field of the Invention
The present invention relates to a method for manufacturing alight emitting device, more particularly, which allows an easier process of individually separating chips.
2. Description of the Related Art
A GaN-based semiconductor having a composition expressed by AlxGayIn(1-x-y)N, where 0≦x≦1, 0≦y≦1, 0≦x+y≦1 is a compound semiconductor material suitable for emitting blue and ultraviolet ray light. Accordingly the GaN-based semiconductor is utilized in a blue or green light emitting diode. The GaN-based LED currently in use is broken down into a planar GaN-based LED and a vertical GaN-based LED. The planar GaN-based LED has p- and n-electrodes in an upper part thereof facing the same direction. Thus, to achieve a sufficient light emitting area, the LED device should be relatively large-sized. Also, due to proximity between the p- and n-electrodes, the planar GaN-based LED is susceptible to electrostatic discharge (ESD).
A vertical GaN-based LED may be employed in place of the planar GaN-based LED with the aforesaid drawbacks. In the vertical GaN-based LED, the p- and n-electrodes are formed on opposed faces between GaN-based epitaxial layers. In a process to manufacture the vertical GaN-based LED, typically, a conductive substrate (e.g. a Si or GaAs substrate) is bonded and an insulating substrate (e.g. a sapphire substrate) is separated. The Korean Patent Application Publication No. 2004-58479 discloses a method for manufacturing a vertical GaN-based LED which involves processes of bonding the Si substrate, separating the sapphire substrate and dicing the Si substrate.
FIGS. 1a to 1f are cross-sectional views illustrating a method for manufacturing a vertical GaN-based light emitting diode according to the prior art. First, referring to FIG. 1a, an n-type clad layer 15a, an active layer 15b and a p-typ clad layer 15c are sequentially formed on a sapphire substrate 11 to obtain a light emitting structure 15. Then, as shown in FIG. 1b, a trench 20 is formed to separate the light emitting structure 15 into individual device areas and then a p-electrode 16 is formed on the p-type clad layer 15c of each device area. Subsequently, as shown in FIG. 1c, a conductive substrate 21 of e.g. Si is bonded to the p-electrode 16 via a conductive adhesive layer of e.g. Au 17. Next, a laser beam 18 is irradiated to separate the sapphire substrate 11 by laser lift-off. This produces a structure having the sapphire substrate 11 removed therefrom, as shown in FIG. 1d. Then, as shown in FIG. 1e, an n-electrode 19 is formed on the n-type clad layer 15a. Thereafter, as shown in FIG. 1f, the resultant structure of FIG. 1e is cut into individual chips (chip separation process). This produces a plurality of vertical light emitting diodes 10 at the same time.
In this conventional method, the conductive substrate 21 is cut into individual devices to separate chips. However to cut the conductive substrate 21 necessitates complicated processes such as dicing, scribing and breaking. Here, in the dicing process, the substrate 21 is cut with a cutting wheel. Therefore, this cutting process increases manufacturing costs and delays an overall process. Moreover, the Si substrate or GaSs substrate employed as the conductive substrate 21 releases heat poorly due to low thermal conductivity thereof, also degrading device properties when a high current is applied. Further, the conductive substrate 21 is bonded at a high temperature of 200° C. or more so that the light emitting structure 15 is prone to cracks. In addition to the GaN-based LED, this problem may arise in manufacturing the vertical LED adopting other group III-V AlGaInP-based or AlGaAs-based compound semiconductor.